Conductive Polymer Composition with a Dual Crosslinker System for Capacitors

ABSTRACT

A capacitor with improved electronic properties is described. The capacitor has an anode, a dielectric on said anode and a cathode on the dielectric. The cathode has a conductive polymer defined as —(CR 1 R 2 CR 3 R 4 —) x — wherein at least one of R 1 , R 2 , R 3  or R 4  comprises a group selected from thiophene, pyrrole or aniline with the proviso that none of R 1 , R 2 , R 3  or R 4  contain —SOOH or COOH; a organofunctional silane; and an organic compound with at least two functional groups selected from the group consisting of carboxylic acid and epoxy.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority to pending U.S. Provisional PatentApplication No. 61/857,878 filed Jul. 24, 2013.

BACKGROUND

The present invention is related to an improved polymerization methodfor preparing solid electrolytic capacitors. More specifically, thepresent invention is related to an improved method of forming a solidelectrolyte capacitor and an improved capacitor formed thereby. Evenmore specifically, the present invention is related to a capacitorcomprising improved crosslinking within the conductive polymeric cathodelayer thereby improving adhesion as evidenced by improved ESR and ESRstability.

Electroconductive polymers are widely used in capacitors, solar cellsand LED displays. The electroconductive polymers include polypyrrole,polythiophene and polyaniline. Among them, the most commerciallysuccessful conductive polymer is poly(3,4-ethylenedioxy thiophene)(PEDOT). One way to apply PEDOT is by forming the PEDOT polymer viain-situ chemical or electrochemical polymerization. The other way is touse it as a PEDOT dispersion preferably with a polyanion, which has muchbetter solubility than PEDOT itself. More particularly,PEDOT-polystyrene sulfonic acid (PEDOT-PSSA) dispersion has gained a lotof attention due to its high conductivity and good film formingproperty.

Today, almost all electronic components are mounted to the surface ofcircuit boards by means of infra-red (IR) or convection heating of boththe board and the components to temperatures sufficient to reflow thesolder paste applied between copper pads on the circuit board and thesolderable terminations of the surface mount technology (SMT)components. A consequence of surface-mount technology is that each SMTcomponent on the circuit board is exposed to soldering temperatures thatcommonly dwell above 180° C. for close to a minute, typically exceeding230° C., and often peaking above 250° C. If the materials used in theconstruction of capacitors are vulnerable to such high temperatures, itis not unusual to see significant positive shifts in ESR leading tonegative shifts in circuit performance. SMT reflow soldering is asignificant driving force behind the need for capacitors havingtemperature-stable ESR.

Equivalent Series Resistance (ESR) stability of the capacitors requiresthat the interface between the cathode layer, cathodic conductivelayers, conductive adhesive, and leadframe have good mechanicalintegrity during thermo mechanical stresses. Solid electrolyticcapacitors are subject to various thermomechanical stresses duringassembly, molding, board mount reflow, etc. During board mount thecapacitors are often subjected to temperatures above 250° C. Theseelevated temperatures create stresses in the interfaces due tocoefficient of thermal expansion (CTE) mismatches between adjacentlayers. The resultant stress causes mechanical weakening at theinterfaces. In some cases this mechanical weakening causes delamination.Any physical separation of the interfaces causes increases in electricalresistance between the layers and thus an increased ESR in the finishedcapacitor.

PEDOT-PSSA polymer film often does not have enough mechanical strengthor sufficient adhesion to the underlying surface. In capacitors, poorfilm quality and adhesion results in poor ESR or poor ESR stabilityunder processing conditions. Polymeric binders can be added to enhancethe mechanical properties of the PEDT-PSSA film and adhesion to theanode. In U.S. Pat. No. 6,987,663, which is incorporated herein byreference, the conductive polymer coating included at least onepolymeric organic binder. In U.S. Pat. No. 7,990,684, which isincorporated herein by reference, the conductive polymer coatingcontains a Novolak polymer resin and a sulfonated polyester as binders.

The polymer binder may be formed “in situ” during the drying step asdescribed in U.S. Published Patent Application 2012/0256117, which isincorporated herein by reference, wherein described is a polymerdispersion of PEDOT-PSSA comprising a polyhydric alcohol and an organicsubstance having two or more functional groups which can bepolycondensed with the polyhyric alcohol to form a polymer binder “insitu”.

Another problem associated with PEDOT-Polyanion, especially PEDOT-PSSAconductive polymer film is the hydroscopic property of the polyanions.Polyanions readily absorb water during the capacitor processing steps(for example, dipping coating cycles) or moisture from the environment,and resulted in swelling of the conductive polymer film. The swollenconductive film is typically subjected to drying steps later on. Theswelling/shrinking cycles often cause the conductive polymer film todelaminate from the substrate. In capacitor application, it ismanifested as deteriorated performance such as positive ESR shift.

EP 0844284, which is incorporated herein by reference, describes aconductive polymer self-doped by —SOOH and/or —COOH functional groupswherein the self-doping groups are on the conductive polymer structure.An advantage of using self-doped conductive polymer over external dopedpolymer as in the case of PEDT-polyanion dispersion, is the eliminationof polyanions which are detrimental to moisture resistance. Still, theseself-doped polymer films have poor water or solvent resistingproperties. The conductive polymer film's water resistance property canbe improved by reacting the self doping groups —SOOH or —COOH with acrosslinking compound having 2 or more functional groups such as ahydroxyl, a silanol, a thiol, an amino or an epoxy group.

For more hydroscopic externally doped PEDOT-PSSA, U.S. Published PatentApplication 2010/0091432, which is incorporated herein by reference,described the use of organic substance with a mono epoxy group inPEDOT-PSSA to improve its water resistance. In comparison, an epoxycompound having multiple epoxy groups in the conductive polymercomposition resulted in inferior water resistance property and higherESR.

In spite of the ongoing efforts there is still a significant problemassociated with coating stability in electrolytic capacitors utilizingconductive polymer cathodes. Further advances in the art are providedherein.

SUMMARY

It is an object of the invention to provide an improved capacitor.

A particular feature of the invention is a capacitor with lower ESR andimproved ESR stability, particularly, after heating.

These and other advantages, as will be realized, are provided in acapacitor. The capacitor has an anode, a dielectric on said anode and acathode on the dielectric. The cathode has a conductive polymer definedas —(CR¹R²CR³R⁴—)_(x)— wherein at least one of R¹, R², R³ or R⁴comprises a group selected from thiophene, pyrrole or aniline with theproviso that none of R¹, R², R³ or R⁴ contain —SOOH or COOH; aorganofunctional silane; and an organic compound with at least twofunctional groups selected from the group consisting of carboxylic acidand epoxy.

Yet another embodiment is provided in a conductive polymer dispersioncomprising a solvent, a conductive polymer, an organofunctional silaneand an organic compound with two or more functional groups selected fromthe group consisting of epoxy and carboxylic acid.

Yet another embodiment is provided in a method for preparing a capacitorcomprising:

forming an anode;forming a dielectric on the anode; andforming a cathode on the dielectric comprising:forming a conductive layer comprising:a conductive polymer defined as —(CR¹R²CR³R⁴—)_(x)— wherein at least oneof R¹, R², R³ or R⁴ comprises a group selected from thiophene, pyrroleor aniline with the proviso that none of R¹, R², R³ or R⁴ contain —SOOHor COOH;an organofunctional silane; andan organic compound with two or more functional groups selected from thegroup consisting of epoxy and carboxylic acid.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of an embodiment of theinvention.

FIG. 2 is a schematic partial cross-sectional view of an embodiment ofthe invention.

FIG. 3 is a flow chart representation of an embodiment of the invention.

DESCRIPTION

The present invention is directed to a dual crosslinker system includingthe combination of two crosslinking agents, an organofunctional silaneand an organic compound with at least two functional groups selectedfrom the group consisting of epoxy and carboxylic acid which provides asurprising synergy when compared with single crosslinker systems. Inaddition, by using this dual crosslinker system, polymeric organicbinders can be avoided in some embodiments, while still achieving lowerESR and improved ESR stability.

The invention will be described with reference to the various figuresforming an integral non-limiting component of the disclosure. Throughoutthe disclosure similar elements will be numbered accordingly.

An embodiment of the invention is illustrated in cross-sectionalschematic side view in FIG. 1. In FIG. 1, a capacitor, generallyrepresented at 10, comprises an anode, 12, with an anode lead wire, 14,extending therefrom or attached thereto. The anode lead wire ispreferably in electrical contact with an anode lead, 16. A dielectric,18, is formed on the anode and preferably the dielectric encases atleast a portion, and preferably the entire, anode. A cathode, 20, is onthe dielectric and encases a portion of the dielectric with the provisothat the cathode and anode are not in direct electrical contact. Acathode lead, 22, is in electrical contact with the cathode. In manyembodiments it is preferred to encase the capacitor in a non-conductiveresin, 24, with at least a portion of the anode lead and cathode leadexposed for attachment to a circuit board as would be readily understoodby one of skill in the art. The cathode may comprise multiplesub-layers. The present invention is directed to improvements in thecathode layer, 20, and more particularly to the formation of the cathodelayer.

An embodiment of the invention is illustrated in partial cross-sectionalschematic view in FIG. 2. In FIG. 2, the cathode, 20, comprises multipleinterlayers, 201-204, which are illustrated schematically, wherein thecathode is formed on the dielectric, 18. While not limited thereto thecathode interlayers are preferably selected from layers of conductivepolymer, carbon containing layers and metal containing layers mostpreferably in sequential order. In a particularly preferred embodiment afirst interlayer, 201, is at least one conductive polymer layer formedeither by in-situ polymerization or by repeated dipping in a slurry ofconductive polymer with at least partial drying between dips. It is wellunderstood that soldering a lead frame, or external termination, to apolymeric cathode is difficult. It has therefore become standard in theart to provide conductive interlayers which allow for solder adhesion. Asecond interlayer, 202, which is preferably at least one carboninterlayer, is typically applied to the conductive polymer interlayer,201. The carbon interlayer, or series of carbon interlayers, providesadhesion to the conductive polymer interlayer and provides a layer uponwhich a third interlayer, which is preferably at least one metalcontaining interlayer, 203, will adequately adhere. Particularlypreferred metal containing layers comprise silver, copper or nickel. Themetal interlayer allows external terminations, such as a cathode lead tobe attached to the cathodic side of the capacitor such as by solder oran adhesive interlayer, 204.

An embodiment of the invention is illustrated in flow chart form in FIG.3. In FIG. 3, the method of forming a solid electrolytic capacitor ofthe instant invention is illustrated. In FIG. 3, an anode is provided at32. A dielectric is formed on the surface of the anode at 34 with aparticularly preferred dielectric being the oxide of the anode. Acathode layer is formed at 36 wherein the cathode comprises multipleinterlayers. Interlayers may include at least one conducting polymerlayer wherein the intrinsically conducting polymer is either formedin-situ or the layer is formed by coating with a slurry comprisingintrinsically conducting polymer. The interlayers also preferablycomprise at least one carbon containing layer and at least one metalcontaining layer. Anode and cathode leads are attached to the anode andcathode respectively at 38 and the capacitor is optionally, butpreferably, encased at 40 and tested.

The conductive polymer layer may be formed in a single step wherein aslurry is applied comprising at least the conductive polymer andoptionally the crosslinkers, and any adjuvants such as binder, dopant,organic acid and the like. Alternatively, the conductive polymer layermay be formed in multiple steps wherein components of the layer areapplied separately. In one embodiment a conductive polymer layer iscoated after coating one or both crosslinkers. In another embodiment theconductive polymer is applied in concert with a first crosslinkerfollowed by application of the second crosslinker. Separating thecomponents and applying them sequentially instead of in concert isbeneficial in some embodiments since the mixture of conductive polymerand crosslinkers may react prematurely thereby decreasing the pot-lifeof the slurry. In a particularly preferred embodiment the conductivepolymer and glycidyl silane are in one slurry with the secondcrosslinker, such as glycidyl ether, applied separately and preferablyafter application of slurry containing the conductive polymer.

The anode is a conductor preferably selected from a metal or aconductive metal oxide. More preferably the anode comprises a mixture,alloy or conductive oxide of a valve metal preferably selected from Al,W, Ta, Nb, Ti, Zr and Hf. Most preferably the anode comprises at leastone material selected from the group consisting of Al, Ta, Nb and NbO.An anode consisting essentially of Ta is most preferred. Conductivepolymeric materials may be employed as an anode material. Particularlypreferred conductive polymers include polypyrrole, polyaniline andpolythiophene.

The cathode is a conductor preferably comprising a conductive polymericmaterial. Particularly preferred conductive polymers includeintrinsically conductive polymers most preferably selected frompolypyrrole, polyaniline and polythiophene. Metals can be employed as acathode material with valve metals being less preferred. The cathode mayinclude multiple interlayers wherein adhesion layers are employed toimprove adhesion between the conductor and the termination. Particularlypreferred adhesion interlayers include carbon, silver, copper, oranother conductive material in a binder. The cathode is preferablyformed by dipping, coating or spraying either a slurry of conductivepolymer or a conductive polymer precursor which is polymerized by anoxidant as known in the art. Carbon and metal containing layers aretypically formed by dipping into a carbon containing liquid or bycoating. The carbon containing layers and metal containing layers can beformed by electroplating and this is a preferred method, in oneembodiment, particularly for the metal containing layer.

The dielectric is a non-conductive layer which is not particularlylimited herein. The dielectric may be a metal oxide or a ceramicmaterial. A particularly preferred dielectric is the oxide of a metalanode due to the simplicity of formation and ease of use. The dielectricis preferably formed by dipping the anode into an anodizing solutionwith electrochemical conversion. Alternatively, a dielectric precursorcan be applied by spraying or printing followed by sintering to form thelayer. When the dielectric is an oxide of the anode material dipping isa preferred method whereas when the dielectric is a different material,such as a ceramic, a spraying or coating technique is preferred.

The anode lead wire is chosen to have low resistivity and to becompatible with the anode material. The anode lead wire may be the sameas the anode material or a conductive oxide thereof. Particularlypreferred anode lead wires include Ta, Nb and NbO. The shape of theanode lead wire is not particularly limiting. Preferred shapes includeround, oval, rectangular and combinations thereof. The shape of theanode lead wire is preferably chosen for optimum electrical properties.

The conductive polymer has a backbone defined as—(CR¹R²—CR³R⁴—)_(x)—wherein at least one of R¹, R², R³ or R⁴ comprises agroup selected from thiophene, pyrrole or aniline which may besubstituted wherein subscript x is at least 2 to no more than 1000. Noneof R¹, R², R³ or R⁴ contain —SOOH or COOH. Hydrogen and lower alkyls ofless than five carbons are particularly suitable. Thiophenes areparticularly preferred with poly(3,4-ethylenedioxythiophene) being mostpreferred.

The conductive polymer layer comprises two crosslinkers which functionsynergistically to provide an improved capacitor with lower ESR. Thefirst crosslinker is an organofunctional silane and the second is anorganic compound with at least two functional groups selected from epoxyand carboxylic acid. Organofunctional silane, more particularly,glycidyl silane crosslinkers have been taught in the art, however, it iswidely known that excessive amounts of silane crosslinker makes driedconductive polymer film rigid and fragile, consequently ESR and ESRstability suffer with increased concentration of silane. Therefore, theartisan has been limited to the amount of crosslinking to be achievedsince the concentration of silane in the conductive polymer must belimited to minimize ESR. Organofunctional silane has never reached thetheoretical potential as a crosslinker in capacitors.

Organic compounds with one epoxy group have been taught in the art toenhance water resistance, as described in U.S. Published PatentApplication 2010/0091432. However, if more than one epoxy group isutilized the water resistance is not improved as much. The teaching fromprior art is that crosslinking compounds with more than one functionalcrosslinking group become sterically bulky after the crosslinkingreaction, which prevents them from spreading into the conductive polymerhomogeneously and therefore they fail to improve the water resistanceeffectively. Organic compounds with more than one epoxy group havetherefore been considered unsuitable for use in electronic capacitorssince the polymeric cathode layer tends to delaminate due to excessivewater absorption thereby rendering the capacitor useless.

It is surprising that the combination of organofunctional silane andorganic compound with more than one crosslinking group, especially morethan one epoxy group, react synergistically providing a much lower ESRat a given level of organofunctional silane without an increase in waterabsorption as would be expected, particularly for the epoxy crosslinkingcompound with more than one epoxy group. This unexpected synergismallows for the use of a higher concentration of organofunctional silaneand epoxy crosslinking compound combined, and therefore morecrosslinking sites, than previously considered possible. The increase incrosslinking increases the structural integrity of the conductivepolymer layer as evidenced by lower ESR.

It is even more surprising that the combination of organofunctionalsilane and organic compound with more than one carboxylic group alsoshows a synergistic function and provides a much lower ESR at a givenlevel of organofunctional silane. Carboxylic groups are not consideredreactive toward —SOOH or —COON groups under normal capacitor processingconditions as described in “Mixed sulfonic-carboxylic anhydrides. I.Synthesis and thermal stability. New syntheses of sulfonic anhydrides”,by Yehuda Mazur, Michael H. Karger, J. Org. Chem., 1971, 36 (4), pp528-531. The ESR improvement may be attributed to reactions between theorganofuncational silane and the carboxylic crosslinking compound, andother components of the conductive polymer dispersion. Herein, althoughwe discuss dual crosslinker systems of organosilane and epoxycrosslinking compound or dual crosslinker systems of organosilane andcarboxylic crosslinking system, a multi-crosslinker system than contains3, or 4, or even more crosslinkers is envisioned.

The organofunctional silane concentration may range from about 0.05 wt %to about 10 wt % of the conductive polymer dispersion at a percentsolids of about 0.2 to 10 wt %. More preferably, the organofunctionalsilane concentration may range from about 0.1 wt % to about 5 wt % ofthe conductive polymer and even more preferably about 0.1 wt % to about2 wt %.

Organofunctional silane is defined by the formula:

XR₁Si(R₃)_(3-n)(R₂)_(n)

wherein X is an organic functional group such as amino, epoxy,anhydride, hydroxy, mercapto, sulfonate, carboxylate, phosphonate,halogen, vinyl, methacryloxy, ester, alkyl, etc; R₁ is an aryl or alkyl(CH₂), wherein m can be 0 to 14; R₂ is individually a hydrolysablefunctional group such as alkoxy, acyloxy, halogen, amine or theirhydrolyzed product; R₃ is individually an alkyl functional group of 1-6carbons; n is 1 to 3.

The organofunctional silane can also be dipodal, define by the formula:

Y(Si(R₃)_(3-n)(R₂)_(n))₂

wherein Y is any organic moiety that contains reactive or nonreactivefunctional groups, such as alkyl, aryl, sulfide or melamine; R₃, R₂ andn are defined above. The organofunctional silane can also bemulti-functional or polymeric silanes, such as silane modifiedpolybutadiene, or silanbe modified polyamine, etc.

Examples of organofunctional silane include3-glycidoxypropyltrimethoxysilane, 3-am inopropytriethoxysilane, aminopropylsilanetriol, (triethoxysilyl)propylsuccinic anhydride,3-mercaptopropyltrimethoxysilane, vinyltrimethoxysilane,3-methacryloxypropyltrimethoxysilane, 3-trihydroxysilyl-1-propanesulfonic acid, octyltriethyoxysilane, bis(triethoxysilyl)octane, etc.The examples are used to illustrate the invention and should not beregarded as conclusive.

A particularly preferred organofunctional silane is glycidyl silanedefined by the formula:

wherein R₁ is an alkyl of 1 to 14 carbons and more preferably selectedfrom methyl ethyl and propyl; and each R₂ is independently an alkyl orsubstituted alkyl of 1 to 6 carbons.

A particularly preferred glycidyl silane is3-glycidoxypropyltrimethoxysilane defined by the formula:

which is referred to herein as “Silane A” for convenience.

The second crosslinker, which is an organic compound with at least twofunctional groups selected from epoxy and carboxylic acid, has aconcentration preferred range from about 0.1 wt % to about 10 wt % ofthe conductive polymer dispersion at a percents solids of about 0.2 toabout 10 wt %. More preferably, the glycidyl ether concentration mayrange from about 0.2 wt % to about 5 wt % of the conductive polymer andeven more preferably about 0.2 wt % to about 2 wt %.

The second crosslinker with at least two epoxy groups is referred toherein as an epoxy crosslinking compound and is defined by the formula:

wherein the X is an alkyl or substituted alkyl of 0-14 carbons,preferably 0-6 carbons; an aryl or substituted aryl, an ethylene etheror substituted ethylene ether, polyethylene ether or substitutedpolyethylene ether with 2-20 ethylene ether groups or combinationsthereof. A particularly preferred substitute is an epoxy group.

Examples of epoxy crosslinking compounds having more than one epoxygroups include ethylene glycol diglycidyl ether (EGDGE), propyleneglycol diglycidyl ether (PGDGE), 1,4-butanediol diglycidyl ether(BDDGE), pentylene glycol diglycidyl ether, hexylene glycol diglycidylether, cyclohexane dimethanol diglycidyl ether, resorcinol glycidylether, glycerol diglycidyl ether (GDGE), glycerol polyglycidyl ethers,diglycerol polyglycidyl ethers, trimethylolpropane polyglycidyl ethers,sorbitol diglycidyl ether (Sorbitol-DGE), sorbitol polyglycidyl ethers,polyethylene glycol diglycidyl ether (PEGDGE),polypropylene glycoldiglycidyl ether, polytetramethylene glycol diglycidyl ether,di(2,3-epoxypropyl) ether, 1,3-butadiene diepoxide, 1,5-hexadienediepoxide, 1,2,7,8-diepoxyoctane, 1,2,5,6-diepoxycyclooctane, 4-vinylcyclohexene diepoxide, bisphenol A diglycidyl ether, maleimide-epoxycompounds, etc.

A preferred epoxy crosslinking compound is glycidyl ether, defined bythe formula:

wherein R₃ is an alkyl or substituted alkyl of 1-14 carbons, preferably2-6 carbons; an ethylene ether or polyethylene ether with 2-20 ethyleneether groups; a alkyl substituted with a group selected from hydroxy, or

or —(CH₂OH)_(x)CH₂OH wherein X is 1 to 14.

Particularly preferred glycidyl ethers are represented by:

The organic compound with at least two carboxylic functional groups isreferred to herein as a carboxylic crosslinking compound.

Examples of carboxylic crosslinking compounds include but are notlimited by, oxalic acid, malonic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,dodecanedioic acid, phthalic acids, maleic acid, muconic acid, citricacid, trimesic acid, polyacrylic acid, etc. Particularly preferredorganic acids are aromatic acid such as phthalic acid, and particularlyortho-phthalic acid, which decreases ESR. The reaction of thecrosslinkable functionality and the crosslinkers occurs at elevatedtemperature which occurs during the normal processing steps of capacitormanufacture.

The construction and manufacture of solid electrolyte capacitors is welldocumented. In the construction of a solid electrolytic capacitor avalve metal preferably serves as the anode. The anode body can be eithera porous pellet, formed by pressing and sintering a high purity powder,or a foil which is etched to provide an increased anode surface area. Anoxide of the valve metal is electrolytically formed to cover up to allof the surfaces of the anode and to serve as the dielectric of thecapacitor. The solid cathode electrolyte is typically chosen from a verylimited class of materials, to include manganese dioxide or electricallyconductive organic materials including intrinsically conductivepolymers, such as polyaniline, polypyrol, polythiophene and theirderivatives. The solid cathode electrolyte is applied so that it coversall dielectric surfaces and is in direct intimate contact with thedielectric. In addition to the solid electrolyte, the cathodic layer ofa solid electrolyte capacitor typically consists of several layers whichare external to the anode body. In the case of surface mountconstructions these layers typically include: a carbon layer; a cathodeconductive layer which may be a layer containing a highly conductivemetal, typically silver, bound in a polymer or resin matrix; and aconductive adhesive layer such as silver filled adhesive. The layersincluding the solid cathode electrolyte, conductive adhesive and layersthere between are referred to collectively herein as the cathode whichtypically includes multiple interlayers designed to allow adhesion onone face to the dielectric and on the other face to the cathode lead. Ahighly conductive metal lead frame is often used as a cathode lead fornegative termination. The various layers connect the solid electrolyteto the outside circuit and also serve to protect the dielectric fromthermo-mechanical damage that may occur during subsequent processing,board mounting, or customer use.

In the case of conductive polymer cathodes the conductive polymer istypically applied by either chemical oxidation polymerization,electrochemical oxidation polymerization or by dipping, spraying, orprinting of pre-polymerized dispersions.

In one embodiment the conductive polymer layer is added as a slurrywherein the slurry is applied to a surface by dipping or coating. Theslurry comprises a solvent, preferably water, the conductive polymer,preferably poly(3,4-ethylenedioxythiophene), a organofunctional silaneand a second crosslinker which is an organic compound with at least twofunctional groups selected from epoxy and carboxylic acid. The solventis preferably polar solvents, such as water, alcohols or acetonitrile,and a mixture of water with polar solvent, with water being the mostpreferred solvent. The solvent is in sufficient ratio to achieve aviscosity suitable for achieving an adequate coating with additionalsolvent being undesirable as the solvent is typically removed afterapplication. The organofunctional silane is preferably present in anamount of 0.0005-0.1000 grams per gram of conductive polymer dispersion.More preferably the organofunctional silane is preferably present in anamount of 0.001-0.050 grams per gram of conductive polymer dispersion.The second crosslinker is preferably present in an amount of 0.001-0.100grams per gram of conductive polymer. More preferably the epoxycrosslinking compound or the carboxylic crosslinking compound ispreferably present in an amount of 0.002-0.050 grams per gram ofconductive polymer.

Apart from the conductive polymer, solvent, organofunctional silane andthe second crosslinker, the slurry may further comprise other additivessuch as conductivity enhancing additives, surface-active substances,coverage enhancing additives and optionally a polymer binder.

Organic acids, and particularly aromatic organic acids are beneficial insome embodiments of the slurry and in the capacitor formed by theslurry. Examples of organic acids can include, formic acid, acetic acid,propanoic acid, oxalic acid, malonic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,dodecanedioic acid, benzoic acid, phthalic acids, maleic acid, muconicacid, etc. Particularly preferred organic acids are phthalic acid, andparticularly ortho-phthalic acid, and benzoic acid both of which furtherdecrease ESR and improve coverage. The slurry preferably comprises0-0.10 grams of organic acid per gram of conductive polymer dispersion.

The slurry may contain surface active additives such as acetylenicdiols, alkyl carboxylates, alkyl sulfate, alkyl sulfonate, fluoroalkylsurfactant or any other surface active substances.

The slurry may contain conductive enhancing additives such asdimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide(DMAc), ethylene glycol, propylene glycol, etc.

The conductive polymer layer preferably comprises a dopant, and morepreferably a polyanion dopant. The polyanion dopant can be present in anamount of up to 90 wt % even though not all polyanion functions as adopant. It is preferable to have a dopant concentration from about 5 wt% to about 30 wt %, more preferably 12 wt % to about 25 wt % and mostpreferably about 21 wt %. Any suitable dopant may be used such as5-sulfosalicylic acid, dodecylbenzenesulfonate, p-toluenesulfonate orchloride. A particularly exemplary dopant is p-toluenesulfonate. Aparticularly preferred polyanion dopant is polystyrene sulfonic acid.

The carbon layer serves as a chemical barrier between the solidelectrolyte and the silver layer. Critical properties of the layerinclude adhesion to the underlying layer, wetting of the underlyinglayer, uniform coverage, penetration into the underlying layer, bulkconductivity, interfacial resistance, compatibility with the silverlayer, buildup, and mechanical properties.

The cathodic conductive layer, which is preferably a silver layer,serves to conduct current from the lead frame to the cathode and aroundthe cathode to the sides not directly connected to the lead frame. Thecritical characteristics of this layer are high conductivity, adhesivestrength to the carbon layer, wetting of the carbon layer, andacceptable mechanical properties.

Throughout the description stated ranges, such as 0-6 or 0.1-0.6 referto all intermediate ranges with the same number of significant figuresas the highest significant figure listed.

EXAMPLES Preparation of PEDOT-PSSA and Conductive Polymer Dipsersion

A 4 L plastic jar, provided with a cooling jacket, was initially chargedwith 125 g of PSSA, 2531 g of DI water, 28.5 g of 1% iron(III) sulphate,and 21.5 g of sodium peroxodisulphate. The contents were mixed using arotor—stator mixing system with perforated stator screen with a roundhole diameter of 1.6 mm. Subsequently, 11.25 g of3,4-ethylenedioxythiophene (PEDOT) was added dropwise. The reactionmixture was sheared continuously with a shear speed of 8000 RPM with therotor-stator mixing system for an additional 23 hours. The dispersionwas treated with cationic and anionic exchange resin and filtered to getPEDOT-PSSA base slurry.

Conductive polymer dispersion was prepared by mixing PEDOT-PSSA baseslurry with other additives and crosslinkers.

Capacitor Manufacturing Example 1

A series of tantalum anodes (33 microfarads, 25V) were prepared. Thetantalum was anodized to form a dielectric on the tantalum anode. Theanode thus formed was dipped into a solution of iron (III)toluenesulfonate oxidant for 1 minute and sequentially dipped intoethyldioxythiophene monomer for 1 minute. The anodes were washed toremove excess monomer and by-products of the reactions after thecompletion of 60 minutes polymerization, which formed a thin layer ofconductive polymer (PEDOT) on the dielectric of the anodes. This processwas repeated until a sufficient thickness was achieved. The conductivepolymer dispersion was applied to form an external polymer layer. Afterdrying, alternating layers of decanediamine toluenesulfonate andconductive polymer dispersion was applied and repeated 4-5 more times.The anodes with conductive polymer layer were washed and dried, followedby sequential coating of a graphite layer and a silver layer to producea solid electrolytic capacitor. Parts were assembled, packaged andsurface mounted. ESR was measured before and after surface mount.

Capacitor Manufacturing Example 2

A series of tantalum anodes (330 microfarads, 6V) were prepared. Thetantalum was anodized to form a dielectric on the tantalum anode. Theanode thus formed was dipped into a solution of iron (III)toluenesulfonate oxidant for 1 minute and sequentially dipped intoethyldioxythiophene monomer for 1 minute. The anodes were washed toremove excess monomer and by-products of the reactions after thecompletion of 60 minutes polymerization, which formed a thin layer ofconductive polymer (PEDOT) on the dielectric of the anodes. This processwas repeated until a sufficient thickness was achieved. Conductivepolymer dispersion was applied to form an external polymer layer. Afterdrying, this process was repeated 2 more times, followed by sequentialcoating of a graphite layer and a silver layer to produce a solidelectrolytic capacitor. Parts were assembled, packaged and surfacemounted. ESR was measured before and after surface mount.

Comparative Example 1

To 120 g of the PEDOT-PSSA conductive polymer was added 4.8 g of DMSOand 0.48 g of 3-glycidoxypropyltrimethoxysilane (Silane A). Theconductive polymer dispersion was mixed in a container by rollingovernight. The solid capacitor was produced following the process inCapacitor Manufacturing Example 1.

Comparative Example 2

Same as Comparative Example 1, except that 0.96 g of Silane A was usedto prepare the conductive polymer dispersion.

Comparative Example 3

Same as Comparative Example 1, except that 1.44 g of Silane A was usedto prepare the conductive polymer dispersion.

Inventive Example 1

To 120 g of the PEDOT-PSSA conductive polymer was added 4.8 g of DMSO,0.48 g of Silane A and 0.96 g of EGDGE. The conductive polymerdispersion was mixed in a container by rolling overnight. The solidcapacitor was produced following the process in Capacitor ManufacturingExample 1.

To 120 g of the PEDOT-PSSA conductive polymer was added 4.8 g of DMSO,0.96 g of Silane A and 0.48 g of EGDGE. The conductive polymerdispersion was mixed in a container by rolling overnight. The solidcapacitor was produced following the process in Capacitor ManufacturingExample 1.

To compare the dual crosslinker system with single crosslinker systemusing glycidyl silane crosslinker a series of comparative polymerslurries were prepared with various amounts of3-glycidoxypropyltrimethoxysilane (Comparative Example 1-3) as presentedin Table 1. A tantalum capacitor was formed using the polymer slurry toform the polymeric cathode layer. Anode and cathode terminations wereformed in identical manner using conventional technologies. As notedtherein, ESR increased with increasing crosslinker which is contrary tothe desire in the art. Inventive samples were prepared using variousamounts of silane crosslinker with various amounts of EDDGE crosslinkeras presented in Table 1. The ESR was measured with the resultsreproduced in Table 1. The results clearly illustrate the synergisticeffect of improved ESR resulting from the inventive dual crosslinkersystem.

TABLE 1 Examples Crosslinkers ESR (mΩ) Comp. 1 Silane A 0.4% 39.77 Comp.2 Silane A 0.8% 44.49 Comp. 3 Silane A 1.2% 46.91 Inv. 1 Silane A 0.4%,30.93 EGDGE 0.8% Inv. 2 Silane A 0.8%, 36.83 EGDGE 0.4%

Comparative Example 4

To 80 g of the PEDOT-PSSA conductive polymer was added 3.2 g of DMSO,0.32 g of Silane A and 2.56 g of a commercial polyester binder (44%aqueous dispersion). The conductive polymer dispersion was mixed in acontainer by rolling overnight. The solid capacitor was producedfollowing the process in Capacitor Manufacturing Example 1.

Comparative Example 5

A commercial PEDOT-PSSA conductive polymer dispersion Clevios™ K fromHeraeus of Leverkusen/Germany (KV2) was used to produce the solidcapacitor following the process in Capacitor Manufacturing Example 1.

Inventive Example 3

To 80 g of the PEDOT-PSSA conductive polymer was added 3.2 g of DMSO,0.32 g of Silane A and 0.64 g of PEGDGE. The conductive polymerdispersion was mixed in a container by rolling overnight. The solidcapacitor was produced following the process in Capacitor ManufacturingExample 1.

Inventive Example 4

Same as Comparative Example 4, except that BDDGE instead of PEGDGE wasused to prepare the conductive polymer dispersion.

Inventive Example 5

Same as Comparative Example 4, except that GDGE instead of PEGDGE wasused to prepare the conductive polymer dispersion.

Inventive Example 6

Same as Comparative Example 4, except that Sorbitol-DGE instead ofPEGDGE was used to prepare the conductive polymer dispersion.

A series of diglycidyl ether crosslinker slurry were prepared in Example3-6 with the components and their levels presented in Table 2.Capacitors were formed using the slurry as in Capacitor ManufacturingExample 1 and the ESR was measured before and after conventionalmounting using conventional surface mount technology (SMT) with a reflowtemperature of 260° C. Comparative Example 4 was identically preparedutilizing Silane A and a commercial polyester binder. Comparativeexample 5 used a commercial polymer slurry KV2. All inventive examplesshowed similarly lower ESR values compared with the two comparativeexamples under the experimental condition. After SMT mounting, allinventive examples showed no detrimental ESR shift and are much morestable than the comparative examples.

TABLE 2 Pre Post Mount Mount SMT ESR Examples Crosslinkers ESR (mΩ) (mΩ)Inv. 3 Silane A 0.4%, 34.99 32.30 PEGDGE 0.8% Inv. 4 Silane A 0.4%,33.31 30.36 BDDGE 0.8% Inv. 5 Silane A 0.4%, 32.82 30.21 GDGE 0.8% Inv.6 Silane A 0.4%, 31.88 29.21 Sorbitol-DGE 0.8% Comp. 4 Silane A 0.4%48.83 58.86 Commercial polyester binder 1.4% Comp. 5 Commercialconductive polymer 32.25 56.54 dispersion (KV2)

Comparative Example 6

To 200 g of the PEDOT-PSSA conductive polymer was added 8 g of DMSO and0.8 g of Silane A. The conductive polymer dispersion was mixed in acontainer by rolling overnight. The solid capacitor was producedfollowing the process in Capacitor Manufacturing Example 1.

Comparative Example 7

To 200 g of the PEDOT-PSSA conductive polymer was added 8 g of DMSO and0.8 g of Silane A. The conductive polymer dispersion was mixed in acontainer by rolling overnight. The solid capacitor was producedfollowing the process in Capacitor Manufacturing Example 2.

Inventive Example 7

To 200 g of the PEDOT-PSSA conductive polymer was added 8 g of DMSO, 0.8g of Silane A and 2 g of o-phthalic acid (PA). The conductive polymerdispersion was mixed in a container by rolling overnight. The solidcapacitor was produced following the process in Capacitor ManufacturingExample 1.

Inventive Example 8

To 200 g of the PEDOT-PSSA conductive polymer was added 8 g of DMSO, 0.8g of Silane A and 2 g of o-phthalic acid (PA). The conductive polymerdispersion was mixed in a container by roller overnight. The solidcapacitor was produced following the process in Capacitor ManufacturingExample 2.

The dual crosslinker system using glycidyl silane crosslinker andphthalic acid crosslinker showed improved ESR and ESR stability relativeto the comparative examples using only the silane crosslinker.

TABLE 3 NB# Crosslinkers ESR (mΩ) Comp. 6 Silane A 0.4% 38.3 Inv. 7Silane A 0.4%, PA 1% 31.8 Comp. 7 Silane A 0.4% 54.6 Inv. 8 Silane A0.4%, PA 1% 28.8

Inventive Example 9

To 80 g of the PEDOT-PSSA conductive polymer was added 3.2 g of DMSO,0.32 g of Silane A and 0.56 g of EGDGE. The conductive polymerdispersion was mixed in a container by rolling overnight. The solidcapacitor was produced following the process in Capacitor ManufacturingExample 1.

Inventive Example 10

Same as Comparative Example 9, except that 0.64 g of GDGE instead ofEGDGE was used to prepare the conductive polymer dispersion.

Inventive Example 11

Same as Comparative Example 9, except that 0.72 g of Sorbitol-DGEinstead of EGDGE was used to prepare the conductive polymer dispersion.

Inventive Example 12

To 80 g of the PEDOT-PSSA conductive polymer was added 3.2 g of DMSO,0.32 g of Silane A, 0.56 g of PA and 0.56 g of EGDGE. The conductivepolymer dispersion was mixed in a container by rolling overnight. Thesolid capacitor was produced following the process in CapacitorManufacturing Example 1.

Inventive Example 13

To 80 g of the PEDOT-PSSA conductive polymer was added 3.2 g of DMSO,0.32 g of Silane A, 0.64 g of GDGE and 0.48 g of PA. The conductivepolymer dispersion was mixed in a container by rolling overnight. Thesolid capacitor was produced following the process in CapacitorManufacturing Example 1.

Inventive Example 14

To 80 g of the PEDOT-PSSA conductive polymer was added 3.2 g of DMSO,0.32 g of Silane A, 0.40 g of PA and 0.72 g of Sorbitol-DGE. Theconductive polymer dispersion was mixed in a container by rollingovernight. The solid capacitor was produced following the process inCapacitor Manufacturing Example 1.

Conductive polymer slurries were prepared as above with, in someinstances, the additional incorporation of ortho-phthalic acid. Theaddition of ortho-phthalic acid had two benefits: further ESR reductionand improved anode edge and corner coverage. The edge and cornercoverage was rated by visual observation and 99% means that all cornersand edges are covered.

TABLE 4 Post 4^(th) 5^(th) Pre Mount Slurry Slurry Mount SMT Cycle CycleESR ESR Cover Cover Examples Crosslinkers (mΩ) (mΩ) age % age % Inv. 9Silane A 0.4% 34.13 34.03 95% 96% EGDGE 0.7% Inv. 10 Silane A 0.4% 34.1534.98 97% 98% GDGE 0.8% Inv. 11 Silane A 0.4% 30.87 30.03 97% 99%Sorbitol-DGE 0.9% Inv. 12 Silane A 0.4% 32.41 29.83 96% 98% EGDGE 0.7%PA 0.7% Inv. 13 Silane A 0.4%, 34.59 31.94 98% 99% GDGE 0.8%, PA 0.6%Inv. 14 silane 0.4%, 31.75 30.50 98% 99% Sorbitol-DGE 0.9%, PA 0.5%

Comparative Example 8

Same as Comparative Example 5.

Inventive Example 15

To 600 g of the PEDOT-PSSA conductive polymer was added 24 g of DMSO and2.4 g of Silane A. The conductive polymer dispersion was mixed in acontainer by rolling overnight. The solid capacitor was producedfollowing the process in Capacitor Manufacturing Example 1, except thatafter the conductive polymer layer was applied, the anode was soaked in2.5% of EGDGE ethanol solution for 5 minute and dried to form acrosslinker coating. The rest of the anode manufacturing processremained the same.

Inventive Example 16

Same as Inventive Example 15, except that 2.5% of Sorbitol-DGE ethanolsolution was used instead of EGDGE ethanol solution.

The dual crosslinker can also be applied separately in two steps. The1^(st) crosslinker Silane A was included in the conductive polymerdispersion, the 2^(nd) crosslinker (glycidyl ether) was applied as aseparate coating afterwards. This process again showed better ESR thanthe commercial conductive polymer dispersion KV2 applied in one stepcoating.

TABLE 5 Pre Post Mount Mount SMT ESR Examples Crosslinker Coating ESR(mΩ) (mΩ) Inv. 15 2.5% EGDGE ethanol solution 31.58 27.62 Inv. 16 2.5%Sorbitol-DGE ethanol 29.23 30.57 solution Comp. 8 Commercial conductivepolymer 36.61 44.41 dispersion (KV2)

The dual crosslinker system demonstrated good ESR and ESR stability whencompared with single crosslinker system or polymeric binders, even inthe situation when one of the crosslinker can't readily crosslink theconductive polymer PEDOT-PSSA itself. The surprisingly good electricalperformance can only be attributed to the synergy of the two differenttypes of crosslinkers, either by crosslinking reactions between them, orwith other components in the conductive polymer dispersion.

The invention has been described with particular reference to preferredembodiments without limit thereto. One of skilled in the art wouldrealize additional embodiments and improvements which are notspecifically enumerated but which are within the scope of the inventionas specifically set forth in the claims appended hereto.

1-32. (canceled)
 33. A conductive polymer dispersion comprising asolvent, a conductive polymer, an organic silane and an organic compoundwith two or more functional groups selected from the group consisting ofepoxy and carboxylic acid.
 34. The conductive polymer dispersion ofclaim 33 wherein said conductive polymer is defined as—(CR¹R²CR³R⁴—)_(x)— wherein at least one of R¹, R², R³ or R⁴ comprises agroup selected from thiophene, pyrrole or aniline with the proviso thatnone of R¹, R², R³ or R⁴ contain —SOOH or COOH.
 35. The conductivepolymer dispersion of claim 34 wherein said conductive polymer ispoly(3,4-ethylenedioxythiophene).
 36. The conductive polymer dispersionof claim 33 comprising 0.0005-0.1 grams of said organofunctional silaneper gram of said conductive polymer dispersion.
 37. The conductivepolymer dispersion of claim 33 comprising 0.001-0.1 grams of saidorganic compound per gram of said conductive polymer dispersion.
 38. Theconductive polymer dispersion of claim 33 further comprising a dopant.39. The conductive polymer dispersion of claim 38 wherein said dopantcomprises a polyanion.
 40. The conductive polymer dispersion of claim 39wherein said polyanion is polystyrene sulfonic acid.
 41. The conductivepolymer dispersion of claim 38 wherein said dopant is present in anamount of 0.05-0.3 grams per gram of said conductive polymer.
 42. Theconductive polymer dispersion of claim 33 wherein said organic silane isa glycidyl silane defined by the formula:

wherein R₁ is an alkyl of 1 to 14; and each R₂ is independently an alkylof 1 to 6 carbons.
 43. The conductive polymer dispersion of claim 42wherein R₁ is selected from the group consisting of methyl, ethyl andpropyl.
 44. The conductive polymer dispersion of claim 42 wherein saidglycidyl silane is:


45. The conductive polymer dispersion of claim 33 wherein saidorganofunctional silane is defined by the formula:XR₁Si(R₃)_(3-n)(R₂)_(n) wherein X is an organic functional groupselected from amino, epoxy, anhydride, hydroxy, mercapto, sulfonate,carboxylate, phosphonate, halogen, vinyl, methacryloxy, ester and alkyl;R₁ is an aryl or (CH₂)_(m) wherein m can be 0 to 14; R₂ is individuallya hydrolysable functional group; R₃ is individually an alkyl functionalgroup of 1-6 carbons; and n is 1 to
 3. 46. The conductive polymerdispersion of claim 45 wherein said hydrolysable functional group isselected from the group selected from alkoxy, acyloxy, halogen andamine.
 47. The conductive polymer dispersion of claim 33 wherein saidorganofunctional silane is defined by the formula:Y(Si(R₃)_(3-n)(R₂)O₂ wherein Y is any organic moiety that containsreactive or nonreactive functional groups such as alkyl, aryl, sulfideor melamine; R₂ is individually a hydrolysable functional group; R₃ isindividually an alkyl functional group of 1-6 carbons; and n is 1 to 3.48. The conductive polymer dispersion of claim 33 wherein saidorganofunctional silane is selected from the group consisting of:3-glycidoxypropyltrimethoxysilane, 3-aminopropytriethoxysilane,aminopropylsilanetriol, (triethoxysilyl)propylsuccinic anhydride,3-mercaptoprpyltrimethoxysilane, vinyltrimethoxysilane,3-metacryloxypropyltrimethoxysilane, 3-trihydroxysilyl-1-propanesulfonic acid and octyltriethyoxysilane.
 49. The conductive polymerdispersion of claim 33 wherein said epoxy crosslinking compoundcomprises at least two epoxy groups.
 50. The conductive polymerdispersion of claim 49 wherein said epoxy crosslinking compound isdefined by the formula:

wherein the X is an alkyl or substituted alkyl of 0-14 carbons, an arylor substituted aryl, an ethylene ether or substituted ethylene ether,polyethylene ether or substituted polyethylene ether with 2-20 ethyleneether groups or combinations thereof.
 51. The conductive polymerdispersion of claim 50 wherein said substitute is an epoxy group. 52.The conductive polymer dispersion of claim 50 wherein alkyl orsubstituted alkyl has 0-6 carbons.
 53. The conductive polymer dispersionof claim 50 wherein said epoxy crosslinking is selected from the groupconsisting of: ethylene glycol diglycidyl ether, propylene glycoldiglycidyl ether, 1,4-butanediol diglycidyl ether, pentylene glycoldiglycidyl ether, hexylene glycol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, resorcinol glycidyl ether, glyceroldiglycidyl ether, glycerol polyglycidyl ethers, diglycerol polyglycidylethers, trimethylolpropane polyglycidyl ethers, sorbitol diglycidylether (Sorbitol-DGE), sorbitol polyglycidyl ethers, polyethylene glycoldiglycidyl ether, polypropylene glycol diglycidyl ether,polytetramethylene glycol diglycidyl ether, di(2,3-epoxypropyl) ether,1,3-butadiene diepoxide, 1,5-hexadiene diepoxide, 1,2,7,8-diepoxyoctane,1,2,5,6-Diepoxycyclooctane, 4-vinyl cyclohexene diepoxide, bisphenol Adiglycidyl ether and an maleimide-epoxy compound.
 54. The conductivepolymer dispersion of claim 33 wherein said epoxy crosslinking compoundis a glycidyl ether.
 55. The conductive polymer dispersion of claim 54wherein said glycidyl ether is defined by the formula:

wherein R₃ is an alkyl or substituted alkyl of 1-14 carbons or anethylene ether.
 56. The conductive polymer dispersion of claim 55wherein said R₃ is an alkyl or substituted alkyl of 2-6 carbons.
 57. Theconductive polymer dispersion of claim 55 wherein said R₃ is apolyethylene ether.
 58. The conductive polymer dispersion of claim 57wherein said polyethylene ether has 1-220 ethylene ether groups.
 59. Theconductive polymer dispersion of claim 54 wherein said R₃ is an alkylsubstituted with a group selected from hydroxy,

and —(CH₂OH)_(x)CH₂OH wherein X is 1 to
 14. 60. The conductive polymerdispersion of claim 54 wherein said glycidyl ether is selected from thegroup consisting of:


61. The conductive polymer dispersion of claim 33 further whereincomprises an carboxylic acid.
 62. The conductive polymer dispersion ofclaim 61 wherein said carboxylic acid is an aromatic acid.
 63. Theconductive polymer dispersion of claim 62 further wherein said aromaticacid is selected from the group consisting of phthalic acid and benzoicacid.
 64. The conductive polymer dispersion of claim 33 wherein saidorganic compound is a carboxylic crosslinking compound with two or morecarboxylic acid groups.
 65. The conductive polymer dispersion of claim64 wherein said carboxylic crosslinking compound is aromatic acid withcarboxylic groups.
 66. The conductive polymer dispersion of claim 65wherein said carboxylic crosslinking compound is selected from the groupconsisting of: oxalic acid, malonic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,dodecanedioic acid, phthalic acids, maleic acid, muconic acid, citricacid, trimesic acid and polyacrylic acid. 67-104. (canceled)